基于51单片机的电子数字钟设计的外文翻译

AT89C51FamilyUser’sGuide1.Features•CompatiblewithMCS-51™Products•4KBytesofIn-SystemReprogrammableFlashMemory–Endurance:1,000Write/EraseCycles•FullyStaticOperation:0Hzto24MHz•Three-levelProgramMemoryLock•128x8-bitInternalRAM•32ProgrammableI/OLines•Two16-bitTimer/Counters•SixInterruptSources•ProgrammableSerialChannel•Low-powerIdleandPower-downModes2.DescriptionTheAT89C51isalow-power,high-performanceCMOS8-bitmicrocomputerwith4KbytesofFlashprogrammableanderasablereadonlymemory(PEROM).ThedeviceismanufacturedusingAtmel’shigh-densitynonvolatilememorytechnologyandiscompatiblewiththeindustry-standardMCS-51instructionsetandpin-out.Theon-chipFlashallowstheprogrammemorytobereprogrammedin-systemorbyaconventionalnonvolatilememoryprogrammer.Bycombiningaversatile8-bitCPUwithFlashonamonolithicchip,theAtmelAT89C51isapowerfulmicrocomputerwhichprovidesahighly-flexibleandcost-effectivesolutiontomanyembeddedcontrolapplications.3.PinConfigurations4.LockDiagramTheAT89C51providesthefollowingstandardfeatures:4KbytesofFlash,128bytesofRAM,32I/Olines,two16-bittimer/counters,afivevectortwo-levelinterruptarchitecture,afullduplexserialport,on-chiposcillatorandclockcircuitry.Inaddition,theAT89C51isdesignedwithstaticlogicforoperationdowntozerofrequencyandsupportstwosoftwareselectablepowersavingmodes.TheIdleModestopstheCPUwhileallowingtheRAM,timer/counters,serialportandinterruptsystemtocontinuefunctioning.ThePower-downModesavestheRAMcontentsbutfreezestheoscillatordisablingallotherchipfunctionsuntilthenexthardwarereset.5.PinDescriptionVCC:Supplyvoltage.GND:Ground.Port0:Port0isan8-bitopen-drainbi-directionalI/Oport.Asanoutputport,eachpincansinkeightTTLinputs.When1sarewrittentoport0pins,thepinscanbeusedashigh-impedanceinputs.Port0mayalsobeconfiguredtobethemultiplexedlow-orderaddress/databusduringaccessestoexternalprogramanddatamemory.InthismodeP0hasinternalpull-ups.Port0alsoreceivesthecodebytesduringFlashprogramming,andoutputsthecodebytesduringprogramverification.Externalpull-upsarerequiredduringprogramverification.Port1:Port1isan8-bitbi-directionalI/Oportwithinternalpull-ups.ThePort1outputbufferscansink/sourcefourTTLinputs.When1sarewrittentoPort1pinstheyarepulledhighbytheinternalpull-upsandcanbeusedasinputs.Asinputs,Port1pinsthatareexternallybeingpulledlowwillsourcecurrent(IIL)becauseoftheinternalpull-ups.Port1alsoreceivesthelow-orderaddressbytesduringFlashprogrammingandverification.Port2:Port2isan8-bitbi-directionalI/Oportwithinternalpull-ups.ThePort2outputbufferscansink/sourcefourTTLinputs.When1sarewrittentoPort2pinstheyarepulledhighbytheinternalpull-upsandcanbeusedasinputs.Asinputs,Port2pinsthatareexternallybeingpulledlowwillsourcecurrent(IIL)becauseoftheinternalpull-ups.Port2emitsthehigh-orderaddressbyteduringfetchesfromexternalprogrammemoryandduringaccessestoexternaldatamemorythatuses16-bitaddresses(MOVX@DPTR).Inthisapplication,itusesstronginternalpull-upswhenemitting1s.Duringaccessestoexternaldatamemorythatuses8-bitaddresses(MOVX@RI),Port2emitsthecontentsoftheP2SpecialFunctionRegister.Port2alsoreceivesthehigh-orderaddressbitsandsomecontrolsignalsduringFlashprogrammingandverification.Port3:Port3isan8-bitbi-directionalI/Oportwithinternalpull-ups.ThePort3outputbufferscansink/sourcefourTTLinputs.When1sarewrittentoPort3pinstheyarepulledhighbytheinternalpull-upsandcanbeusedasinputs.Asinputs,Port3pinsthatareexternallybeingpulledlowwillsourcecurrent(IIL)becauseofthepull-ups.Port3alsoservesthefunctionsofvariousspecialfeaturesoftheAT89C51aslistedbelow:PortPinAlternateFunctionsP3.0RXD(serialinputport)P3.1TXD(serialoutputport)P3.2INT0(externalinterrupt0)P3.3INT1(externalinterrupt1)P3.4T0(timer0externalinput)P3.5T1(timer1externalinput)P3.6WR(externaldatamemorywritestrobe)P3.7RD(externaldatamemoryreadstrobe)Port3alsoreceivessomecontrolsignalsforFlashprogrammingandverification.RST:Resetinput.Ahighonthispinfortwomachinecycleswhiletheoscillatorisrunningresetsthedevice.ALE/PROG______________:AddressLatchEnableoutputpulseforlatchingthelowbyteoftheaddressduringaccessestoexternalmemory.Thispinisalsotheprogrampulseinput(PROG)duringFlashprogramming.InnormaloperationALEisemittedataconstantrateof1/6theoscillatorfrequency,andmaybeusedforexternaltimingorclockingpurposes.Note,however,thatoneALEpulseisskippedduringeachaccesstoexternalDataMemory.Ifdesired,ALEoperationcanbedisabledbysettingbit0ofSFRlocation8EH.Withthebitset,ALEisactiveonlyduringaMOVXorMOVCinstruction.Otherwise,thepinisweaklypulledhigh.SettingtheALE-disablebithasnoeffectifthemicrocontrollerisinexternalexecutionmode.PSEN___________:ProgramStoreEnableisthereadstrobetoexternalprogrammemory.WhentheAT89C51isexecutingcodefromexternalprogrammemory,PSEN____________isactivatedtwiceeachmachinecycle,exceptthattwoPSEN____________activationsareskippedduringeachaccesstoexternaldatamemory.EA_______/VPP:ExternalAccessEnable.EA_______mustbestrappedtoGNDinordertoenablethedevicetofetchcodefromexternalprogrammemorylocationsstartingat0000HuptoFFFFH.Note,however,thatiflockbit1isprogrammed,EA_______willbeinternallylatchedonr